This invention relates to scanning systems and, more particularly, to speed control apparatus for scanning systems.
U.S. Pat. No. 3,848,087 discloses a scanning system utilizing a polygonal mirror for scanning a reflected light beam over a scanning area as each facet of the mirror is rotated into the path of an incident light beam. Conventional analog servo control techniques are employed to control the rotational speed of a drive motor to which the mirror is connected. The motor appears to be a conventional d-c motor.
U.S. Pat. No. 3,809,976 and an article entitled Frequency Controlled AC Motors Challenge DC Drives at Lower HP that appeared in the May, 1975 issue of Product Engineering at pages 29-31 both disclose frequency control of three-phase a-c motors. The article sets forth a number of advantages in using frequency controlled a-c motors over conventional d-c motors.
It would be desirable to provide in a scanning system of the general type disclosed in U.S. Pat. No. 3,848,087 a more effective and efficient method of controlling the rotational speed of the polygonal mirror.